High-voltage rectifying tube



Oct. 5, 1948. M. J. SNILJDERS HIGH VOLTAGE RECTIFYING TUBE Filed Jan. 11, 1947 MARCUS JAN SNI-JDERS INVENTOR AGENT Patented Oct. 5, 1948 HIGH-VOLTAGE RECTIFYING TUBE Marcus Jan Snijders, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn, as trustee Application January 11, 1947, Serial No. 721,647 In the Netherlands November 14, 1945 Section 1, Public Law 690, August 8, 1946 3 Claims. (Cl. 250-275) This invention relates to a rectifier tube comprising a filament cathode and a metal vapour filling for use at high voltages that is to say exceeding 500 volts.

In the known tubes of the aforesaid type the cathode is generally coated with barium oxide or with an oxide of other alkaline earth metal in order to ensure a high emission of electrons. These tubes have a limitation in that notwithstanding all kinds of screening measures, the cathode, due to the bombardment by ions, has a life of not more than some few thousands of hours. If the anode voltage exceeds some few thousands of volts, backfiring frequently occurs because the anode starts to emit at those points at which small quantities of barium which have left the cathode by volatilisation are deposited.

In view of these disadvantages it has already been proposed to replace filament cathode rectifier tubes in systems for broadcasting transmitters by rectifier tubes of the kind having a mercury cathode. Though the latter have a comparatively long life, the working expenses are higher.

It has furthermore been proposed to provide a rectifier tube with a cathode made of tungsten to which a small quantity of thoria is added and to carbonise this cathode so as to ensure a constant supply of metallic thorium from the cathode core during operation. It has been proposed to constitute the filling of the rectifying tube by hydrogen, nitrogen or rare gases but these gases disappear too rapidly to permit the use of low pressures such that the tubes are suitable for use at some few thousands of volts and upwards.

Non-carbonised tungsten-thorium cathodes have also for a long time been known, used with rare gases as well as with a metal vapour-filling, butthe life of such cathodes is short.

A rectifying tube according to the invention is provided with a carbonised tungsten-thorium cathode, the tube being filled with metal vapour.

It has been found by the applicant that tubes according to the invention have a long life and that there is no probability at all of backfiring due to the presence of active cathode material on the anode. Due to the cathode being surrounded with screens, the required filament current energy does not exceed twice the energy required for a cathode activated with alkaline earth metal oxides.

In order that the invention may be clearly understood and readily carried into efiect, it will now be described more fully with reference to the accompanying drawing, which shows a rectifying tube according to the invention.

Referring to the single figure of the drawing, I designates the glass wall of a tube comprising an anode 2, an intermediate electrode 3 and a cathode sleeve 4. The cathode sleeve contains a helical cathode 5. This cathode is made of tungsten having added to it 2% of thoria. This filament wire is carbonised by heating in acetylene at a pressure of about 1 mm. for a time such that about 30% of the cross sectional area of the wire is carbonised. The tube is intended for use at a voltage, to be rectified, of 5 kilovolts; it has a life of many thousands of hours. A drop of mercury 6 at the bottom of the tube ensures the presence of a sufiicient quantity of mercuryvapour.

What I claim is:

l. A high-voltage rectifying tube, comprising a sealed envelope containin an anode, and a cathode which is constituted by a carbonised tungsten-thorium wire and an atmosphere of a metal vapor.

2. A high-voltage rectifying tube, comprising a sealed envelope containing an atmosphere of mercury vapour, and a cathode of tungsten-thorium wire carbonized to an extent within about 30% of its cross-sectional area.

3. A high-voltage, rectifying tube comprising a sealed envelope containing an atmosphere of mercury vapour, an anode, a cathode of tungstenthorium wire carbonized to an extent within about 30% of its cross-sectional area, and a semienclosure for the cathode within the direct path between the cathode and the anode.

MARCUS JAN SNIJDERS.

REFERENCES CITED UNITED STATES PATENTS Name Date Spencer July 27, 1937 Number 

